DESCRIPTION: (Applicant's Abstract) The goal of this application is to define the molecular mechanisms and the role in human colon carcinogenesis of three newly defined and genetically distinct colon cancer "mutator" phenotypes. The applicant has detected these mutator type colon cancers by demonstrating that these cancers have 10-100 fold elevations in their rates of generating spontaneous hprt gene mutations. Two of these phenotypes (comprising six cell lines) are novel, and do not result from defects in previously described DNA mismatch-repair genes. These findings add to earlier studies of mutator mechanisms in colon cancer which the applicant and collaborators have demonstrated that (1) the Hereditary Non-Polyposis Colon Cancer (HNPCC) syndrome is due to inheritance of defective members of the DNA mismatch repair pathway (MMR genes); (2) tumors with MMR gene defects typically display instability of DNA microsatellites (RER tumors); (3) RER cancers also occur among many sporadic cancers, in which case MMR genes are unexpectedly wild type. Thus the applicant proposes that novel RER phenotype cancers are generated by defects not involving any of the known MMR genes. The applicant's studies also demonstrate a second novel mutator mechanism which induces sequence instability in non-RER colon cancers. Work by the applicant also demonstrates that genomic instability in RER and non-RER mutator type tumors is global, inducing hypermutability in expressed genes, as opposed to affecting only generally non-coding microsatellites. The applicant proposes six specific aims: (1) to characterize the specificity of DNA sequences targeted and the sequence spectrum of the spontaneous mutations produced by each of the three mutator phenotypes; (2) to determine the number of complementation groups accounting for the novel mutator phenotypes, and to map the defects inducing these phenotypes to individual chromosomes; (3) to elucidate the susceptibility to specific classes of environmental mutagens of each of the three mutator phenotypes; (4) to determine the relative frequency in Non-RER colon cancer of the novel Non-RER mutator phenotype; (5) to determine whether a transfected wild type DNA repair gene will correct the mutator phenotype and will suppress any other aspect of the transformed phenotype upon transfer into mutator cancer cell lines lacking the wild type gene; and (6) to determine if gene line defects in colon cancer mutator genes can be detected by an increased mutation rate in the patient's lymphocytes.